Calendar bug setting DAY_OF_WEEK in JDK 1.3.1

Question

I cannot find a workaround for this bug:
import java.util.Calendar;
import java.util.Date;
public class Mescal {
public static void main(String[] args) {
Calendar cal = Calendar.getInstance();
cal.set(2002, Calendar.FEBRUARY, 2); // Sat, 2 Feb 2002
cal.set(Calendar.MILLISECOND, 0);
Date d = new Date(cal.getTime().getTime());
Calendar cal2 = Calendar.getInstance();
cal2.setTime(d);
cal.set(cal2.get(Calendar.YEAR),
cal2.get(Calendar.MONTH),
cal2.get(Calendar.DATE));
// cal.set(Calendar.WEEK_OF_MONTH, cal2.get(Calendar.WEEK_OF_MONTH));
System.out.println("start: " + cal.getTime() + " : " + d);
cal.setTime(d);
cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
System.out.println("Set weekday: " + cal.getTime());
cal.set(Calendar.HOUR_OF_DAY, 0);
System.out.println("Set hour: " + cal.getTime());
cal.set(Calendar.MINUTE, 0);
System.out.println("Set minute: " + cal.getTime());
cal.set(Calendar.SECOND, 0);
System.out.println("Set second: " + cal.getTime());
The output is:
start: Sat Feb 02 11:19:18 CET 2002 : Sat Feb 02 11:19:18 CET 2002
Set weekday: Mon Jan 28 11:19:18 CET 2002
Set hour: Mon Dec 31 00:19:18 CET 2001
Set minute: Mon Nov 26 00:00:18 CET 2001
Set second: Mon Oct 29 00:00:00 CET 2001
The problem arises when setting the weekday takes the date back to the previous month. For example, starting off with Feb 9:
start: Sat Feb 09 11:20:50 CET 2002 : Sat Feb 09 11:20:50 CET 2002
Set weekday: Mon Feb 04 11:20:50 CET 2002
Set hour: Mon Feb 04 00:20:50 CET 2002
Set minute: Mon Feb 04 00:00:50 CET 2002
Set second: Mon Feb 04 00:00:00 CET 2002
This has been fixed in JDK1.4Beta2, but obviously we're not going to pin our application on that. There's also a problem with 1.4 that I'll get to in a bit.
The second calendar attempt (seen in code sample but ultimately not used) doesn't make any difference. Although if you don't use setTime and only initialize the calendar using set(int year, int month, int day) then setting the weekday sets it to the 1st week of the month.
For example:
Calendar cal = Calendar.getInstance();
cal.set(2002, Calendar.FEBRUARY, 13); // Sat, 2 Feb 2002
cal.set(Calendar.MILLISECOND, 0);
System.out.println("start: " + cal.getTime());
cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
//rest of code is same
produces:
start: Wed Feb 13 11:38:20 CET 2002
Set weekday: Mon Feb 04 11:38:20 CET 2002
Set hour: Mon Feb 04 00:38:20 CET 2002
Set minute: Mon Feb 04 00:00:20 CET 2002
Set second: Mon Feb 04 00:00:00 CET 2002
The bug (?) in JDK1.4Beta2:
if you set WEEK_OF_YEAR, then the date is advanced one.
Calendar cal = Calendar.getInstance();
cal.set(2002, Calendar.FEBRUARY, 13); // Sat, 2 Feb 2002
cal.set(Calendar.MILLISECOND, 0);
cal.setFirstDayOfWeek(Calendar.SUNDAY);
Date d = new Date(cal.getTime().getTime());
Calendar cal2 = Calendar.getInstance();
cal2.setTime(d);
// cal.set(cal2.get(Calendar.YEAR),
// cal2.get(Calendar.MONTH),
// cal2.get(Calendar.DATE));
cal.set(Calendar.WEEK_OF_YEAR, cal2.get(Calendar.WEEK_OF_YEAR));
// System.out.println("start: " + cal.getTime() + " : " + d);
// cal.setTime(d);
System.out.println("start: " + cal.getTime());
Gives you:
start: Thu Feb 14 11:41:37 CET 2002
Set weekday: Mon Feb 11 11:41:37 CET 2002
Set hour: Mon Feb 11 00:41:37 CET 2002
Set minute: Mon Feb 11 00:00:37 CET 2002
Set second: Mon Feb 11 00:00:00 CET 2002
If you comment out the line cal.set(Calendar.WEEK_OF_YEAR
then the first line of output reads:
start: Wed Feb 13 11:38:17 CET 2002
An unholy mess.

Answer 1

Hi,
I had the same bug as you one week ago... though i never come up with a neat solution, i used several loops to counter this. Its works nicely, but the logic is messy. Here's the code:
Calendar c =new GregorianCalendar();
int first=2002;               
int second=2;               
c.set(Calendar.YEAR,first);
c.set(Calendar.MONTH,second-1); //setting it to feburary
//getting the month after i set
int m = c.get(Calendar.MONTH);
//testing if it has 31 days in the month     
c.set(Calendar.DATE,31);      
//if the month doesnt have 31 days, the month will be
//march as java set it the the next month     
int m1 = c.get(Calendar.MONTH);      
int d = c.get(Calendar.DATE);
System.out.println("month1 is "+m1);
if(m1!=m)
//if m and m1 doesnt match means the month
//doesnt have 31 days
{//if
     //set the month back to the desire month
     c.set(Calendar.MONTH,second-1);
     //test the month for 30 days               c.set(Calendar.DATE,30);
                         m1 = c.get(Calendar.MONTH);
                         d = c.get(Calendar.DATE);
                         System.out.println("month1 is "+m1);
     if(m1!=m)
                              {//if
                                   c.set(Calendar.MONTH,second-1);
                                   c.set(Calendar.DATE,29);
                                   m1 = c.get(Calendar.MONTH);
                                   d = c.get(Calendar.DATE);
                              System.out.println("month1 is "+m1);
                                   if(m1!=m)
                                   {//if     
                                   c.set(Calendar.MONTH,second-1);
                                   c.set(Calendar.DATE,28);
                                   m1 = c.get(Calendar.MONTH);
                                   d = c.get(Calendar.DATE);
System.out.println("month1 is "+m1);
                                                                           }//end if
                              }//end if
}//end if
}//end if